Diesel engine usage for passenger car application is increasing due to the benefit of better fuel economy. Further, gasoline engines are increasing compression ratios to improve the fuel efficiency. As a result, diesel and gasoline engine accessory drive systems have to overcome the vibrations of greater magnitude from crankshafts due to above mentioned changes in engines.
With increased crankshaft vibration in addition to high acceleration/deceleration rates and high alternator inertia the engine accessory drive system is often experiencing belt chirp noise due to belt slip. This will also reduce the belt operating life.
Crankshaft isolators and alternator decouplers/isolators have been widely used for engines with high angular vibration to filter out vibration in engine operation speed range. However, although a crankshaft isolator can function very well in engine running speed range; it still presents problems during engine start-up or shut-down due to the natural frequency of the isolator itself.
An alternator decoupler/isolator can eliminate the belt slipping issue at an alternator pulley, but it cannot resolve belt slip taking place at the crankshaft pulley. For some engines, both a crankshaft isolator and alternator decoupler/isolator has to be used together. Unfortunately, this adds to the cost of the accessory drive system significantly and often vehicle manufacturers are not willing to pay for it.
Representative of the art is U.S. Pat. No. 6,044,943 which discloses a crankshaft decoupler has a mounting hub, a pulley rotatably mounted on the mounting hub, an annular carrier mounted within said pulley, a biasing device mounted therebetween, and a one way clutch mounted between the annular carrier and the pulley. The biasing device cushions the belt drive from crankshaft impulses and lowers the angular resonant frequency of the belt system. The one way clutch prevents sudden reversal of the belt tension in the drive due to start/stop of the engine or sudden deceleration of the engine and prevents momentary reverse slip belt squeal as a result of the tensioners' inadequate output for the reverse mode. The one way clutch limits the maximum amount of torque which may be transmitted preventing belt slippage during momentary overload.
What is needed is a decoupling isolator having a flat wire spiral spring engagable with a stop to limit a rotation of the pulley. The present invention meets this need.